It is a matter of common knowledge that water-granulated blast furnace slag has a tendency to harden because the effects of hydration. Utilizing this property, this type of slag is mixed with Portland cement clinkers and pulverized to make low cost blast furnace slag and steel-making slag cement. However, in such cases, water-granulated slag by itself required relatively long periods of time to harden and does not acquire sufficient strength so that such slag tends to be used as an extender for Portland cement and the slag contents of such cements tend to be around 30% or less.
In addition to the type of slag cements referred to above, there is another well-known type of high sulphate slag cement known as the Sealithor variety, but it is not possible to make such a cement in quantity in Japan since suitable water-granulated blast furnace slag cannot be obtained, coagulation and hardening of such cements require relatively long periods of time and the surfaces of such cements, when hardened tend to develop weak areas so that such cements are, in actual practice, not widely used.